1. Field of the Invention
This invention relates to resistance thermometers especially useful for measuring cryogenic temperatures, and more particularly, to glassy metal alloys suitable as temperature sensing elements for resistance thermometers.
2. Description of the Prior Art
In conventional resistance thermometers having a metallic sensing element, the electrical resistivity decreases with decreasing temperature, with both the resistivity and its temperature coefficient reaching very low values when approaching absolute zero. Thus, conventional metallic resistance thermometers, such as platinum, become less sensitive with decreasing temperature and are essentially ineffective below about 20.degree. K.
Glassy metal resistance thermometers have been disclosed in U.S. Pat. No. 3,644,863, issued Feb. 22, 1972 to C.-C. Tsuei. The composition of the temperature sensing elements of these resistance thermometers comprises a matrix of a first component which is a metal of the platinum series (ruthenium, rhodium, palladium, osmium, iridium and platinum) and a second component which is silicon or germanium. To that two-component matrix is added a third component which is selected from the inner members of the first series of transition metals of titanium, vanadium, chromium, manganese, iron and cobalt. The glassy metal temperature sensing elements are formed as splats. The resistivity of these compositions is disclosed as decreasing with decreasing temperature down to some definite critical temperature. Below that critical temperature, however, the direct dependence upon temperature is reversed and the resistivity increases with decreasing temperature. Thus, glassy metal alloys with negative temperature coefficient of resistivity over a usefully wide low temperature range are obtained. However, these palladium-silicon base glassy metal alloy resistance thermometers evidence room temperature resistivities of only about 83 to 150 .mu.ohm-cm and a substantial field-dependent magnetoresistance and hence are not totally suitable in low temperature cryogenic applications.
Novel glassy metal alloys in wire form have been disclosed by H. S. Chen and D. E. Polk in U.S. Pat. No. 3,856,513, issued Dec. 24, 1974. These glassy metal alloys are represented by the formula T.sub.i X.sub.j, where T is at least one transition metal, X is at least one element selected from the group consisting of aluminium, antimony, beryllium, boron, germanium, carbon, indium, phosphorus, silicon and tin, "i" ranges from about 70 to 87 atom percent and "j" ranges from about 13 to 30 atom percent. However, no compositions suitable for use as temperature sensing elements in cryogenic resistance thermometers are disclosed therein.
Glassy metal alloys prepared from compositions in the beryllium-titanium-zirconium system are known; see, e.g., L. E. Tanner et al., Application Ser. No. 709,028, filed July 26, 1976. The glassy alloys comprise about 30 to 55 atom percent Be, 0 to about 58 atom percent Ti, and about 2 to 65 atom percent Zr. The alloys are disclosed as evidencing high strength, low density and good ductility and are useful in applications requiring a high strength-to-weight ratio. No disclosure as to their electrical resistance properties or their suitability as temperature sensing elements in cryogenic resistance thermometers is made, however.